The present disclosure relates to a metal alloy for a component material used in electromagnetic, chemical, shipbuilding, machinery, and other applications, in addition to components, structural materials, and the like, used in an extreme environment and, in particular, to a high-entropy alloy having a composite structure.
Due to technological breakthroughs in industrial technology, metals and alloys according to the related art have limitations in meeting characteristics required for various materials. To satisfy requirements for multi-functionality, as a novel alloy, a new type of material referred to as a high-entropy alloy has recently been proposed and developed.
A high-entropy alloy refers to not a compound formed by reducing free energy due to the formation of an intermetallic compound, but an alloy with a ductile single phase or multi-phase structure formed by reducing total free energy due to a significant increase in configuration entropy by mixing several elements. In other words, a high-entropy alloy refers to not an intermetallic compound or an amorphous alloy with negligible or limited ductility consisting of multi-component alloying elements, but an alloy with solid solution matrix formed by an atomic scale mixture of several alloying elements without any significant preferential attraction between specific elements.
A high-entropy alloy is disclosed in Non-Patent Document 1 (Materials Science and Engineering A, Vol. 375-377, 2004, page 213-218). In Non-Patent Document 1, a multi-element alloy, Fe20Cr20Mn20Ni20Co20, that the researchers expected to form an amorphous phase or complex intermetallic compound, unexpectedly form a single-phase crystalline face-centered cubic (FCC) solid solution, thereby attracting the interest of material scientists and engineers. Most high-entropy alloys exhibit unusual characteristics such as the formation of a single phase structure, even when alloying elements are mixed in similar amounts in a quartenary, quinary, or higher system, in contrast to the conventional alloy systems in which minor additional alloying elements are added to a major alloying element with the content over 60 weight % to 90 weight % in order to induce precipitates or particles. Unique characteristics are also found in an alloy system in which configuration entropy due to mixing is high.
A high-entropy alloy contains four or more types of metallic elements having an atomic content between 5 at. % and 35 at. %, and is an alloy system in which all alloying elements behave as a main element. Due to a similar atomic fraction of elements existing in an alloy, a high degree of mixing entropy is induced. Therefore, instead of the formation of brittle intermetallic compound or an intermediate compound, a solid solution having a stable and simple structure at high temperature is formed.
As prior art related to high-entropy alloys, there are provided Patent Document 1 (U.S. Laid-Open Patent No. US 2013/0108502 A1) and Patent Document 2 (U.S. Laid-Open Patent No. 2009/0074604 A1). In Patent Document 1, disclosed is a high-entropy alloy having a high degree of hardness and high modulus, an alloy system containing five or more types of metallic elements, in which each element such as vanadium (V), niobium (Nb), tantalum (Ta), molybdenum (Mo), titanium (Ti), or the like is included with a deviation of ±15 atomic % or less, and in which there is no distinction between major and minor elements because of the similar atomic contents in the alloy. In addition, the high-entropy alloy is formed as a single phase solid solution having a face-centered cubic and/or body-centered cubic structure. However, in Patent Document 1, different types of relatively expensive and heavy alloying elements are added, and a difficulty in a manufacturing process is expected due to a large difference in melting points among added alloying elements.
Meanwhile, in Patent Document 2, disclosed is a high-entropy alloy having a high degree of hardness, manufactured in a powder metallurgy process using a ceramic phase (representatively, tungsten carbide) and multi-component high-entropy alloy powder. The high-entropy alloy with hard ceramic particles is manufactured with the single phase solid solution matrix embedded with hard ceramic particles, having high strength and excellent high temperature properties. However, in Patent Document 2, since a high temperature process is required when a ceramic material is used to manufacture an alloy with hard ceramic particles, a problem associated with high temperature sintering process such as low toughness is expected to occur due to the presence of the interface defects.